1. Field of the Invention
The invention relates to a substrate support chuck for supporting a workpiece, such as a semiconductor wafer, within a semiconductor wafer processing system. More particularly, the invention relates to a hybrid Johnsen-Rahbek electrostatic chuck for electrostatically clamping a semiconductor wafer to the surface of the chuck during processing of the wafer.
2. Description of the Background Art
Substrate support chucks are widely used to support substrates within semiconductor wafer processing systems. A particular type of chuck used in semiconductor wafer processing systems, such as physical vapor deposition (PVD), amongst other processing systems, is a ceramic electrostatic chuck. These chucks are used to retain semiconductor wafers, or other workpieces, in a stationary position during processing. Such electrostatic chucks contain one or more electrodes embedded within a ceramic chuck body. The ceramic material is typically aluminum nitride or alumina doped with metal oxide such as titanium oxide (TiO.sub.2) or some other ceramic material with similar resistive properties. This form of ceramic is partially conductive, i.e., the material has a relatively low resistivity (e.g., 10.sup.10 ohms-centimeter) at a particular operating temperature.
In use, a wafer rests flush against the surface of the chuck body as a chucking voltage is applied to the electrodes. Because of the conductive nature of the ceramic material, charges migrate through the ceramic material and accumulate proximate contact points between the wafer and the surface of the chuck body. Consequently, the wafer is primarily retained upon the chuck by the Johnsen-Rahbek effect. Such a Johnsen-Rahbek chuck is disclosed in U.S. Pat. No. 5,117,121 issued May 26, 1992 and U.S. Pat. No. 5,463,526 issued Oct. 31, 1995.
One disadvantage of using a Johnsen-Rahbek chuck is that a uniform chucking force depends upon a uniform distribution of contact points between the backside of the semiconductor wafer and the chuck surface. Since the contact point distribution varies from wafer to wafer, similar wafers are not chucked in the same manner. Furthermore, wafer backside materials may vary and consequently cause differences in the chucking force across the wafer as well as from wafer to wafer. As such, the magnitude of the chucking force and its uniformity depends on wafer backside morphology and wafer backside composition.
Therefore, a need exists in the art for an apparatus that reduces the chucking force dependence upon wafer backside morphology and composition.